1. Field of the Invention
The present disclosure relates to a variable resistance nonvolatile memory device which has a resistance value that changes according to application of electrical signal, and a method of manufacturing the same.
2. Description of the Related Art
In recent years, the performance of electronic devices such as mobile information devices and information appliances has advanced with the development of the digital technology. Thus, it is increasingly required to enhance capacity of a nonvolatile memory device, to reduce power consumption in a writing operation or the like, to increase speed in writing and reading operations, and to realize a long lifetime. It has been difficult to meet the above requirements using a flush memory having a conventional floating gate, as there is a limit on miniaturization of such a flush memory. Among nonvolatile memory elements, a so-called variable resistance element uses a variable resistance material as a material of a memory. The variable resistance element can be composed with a simple structure. Therefore, further miniaturization, higher speed, and lower power consumption can be expected, and thus it has been promoted to research and develop such a variable resistance element.
Here, the variable resistance element refers to an element having a property in which a resistance state reversibly changes in response to application of a voltage pulse, and having a capability of nonvolatily storing information by relating the information to each of the resistance states.
More specifically, the variable resistance element has a simple configuration in which a variable resistance layer made of variable resistance material is provided between a lower electrode layer and an upper electrode layer. In a case of a bipolar variable resistance element, a resistance change phenomenon occurs in the variable resistance layer when a voltage pulse having a different polarity is applied between the lower electrode layer and the upper electrode layer (between the electrodes). That is, for example, when a negative voltage pulse is applied between the electrodes, a state of the variable resistance layer becomes a low resistance state. Conversely, when a positive voltage pulse is applied between the electrodes, a state of the variable resistance layer becomes a high resistance state.
For example, this variable resistance element can store two values by allocating “0” to one of the low resistance state and the high resistance state, and “1” to the other thereof. The nonvolatile memory device having the variable resistance element is a memory device in which information corresponding to the resistance state is written to or read from each variable resistance element, by using the property in which the variable resistance layer changes between at least two states of the high resistance state and the low resistance state.
As for a technique regarding the variable resistance element, for example, PCT International Publication Nos. WO2008/149484 and WO2008/059701 each disclose a variable resistance element that has a variable resistance layer including two tantalum oxide layers of different oxygen content atomic percentages.
PCT International Publication No. WO 2008/149484 discloses a nonvolatile memory element including a lower electrode, an upper electrode, and a variable resistance layer interposed between the lower electrode and the upper electrode, and having a resistance value that reversibly changes based on an electrical signal that has a different polarity and is applied between both of the electrodes. The variable resistance layer has a first region that contains a first oxygen-deficient tantalum oxide having a composition represented by TaOx (0<x<2.5), and a second region that contains a second oxygen-deficient tantalum oxide having a composition represented by TaOy (x<y<2.5). The first region and the second region are stacked in a thickness direction of the variable resistance layer.
PCT International Publication No. WO 2008/059701 discloses a nonvolatile memory element including a first metal line; a plug formed on the first metal line and connected to the first metal line; a stacked structure including a lower electrode, an upper electrode, and a variable resistance layer, the stacked structure being formed on the plug which is connected to the lower electrode; a second metal line formed on the stacked structure and directly connected to the upper electrode; and a side wall protective layer covering a side wall of the stacked structure and having an insulating property and an oxygen barrier property. A part of a lower surface of the second metal line is positioned lower than an upper surface of the stacked structure.